Mitsubishi K4M Specifications
| Engine Model: Mitsubishi K4M |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 121.7 cu.in (1.99 L) |
| Rated Engine Power: 42 Hp (31 kW) at 2400 rpm |
| Fuel System Type: Indirect injection |
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The Mitsubishi K4M is a vertical, water-cooled,
4-stroke, inline-4 diesel engine with a displacement of 1.995 liters. As
one of the largest displacement models in the Mitsubishi K-series diesel
family, this engine serves as a heavy-duty workhorse in mid-sized
tractors, larger mini-excavators, and specialized turf equipment. The
K4M is an indirect injection (swirl chamber) diesel, a design choice
that favors smooth operation, lower combustion noise, and reduced
emissions over absolute fuel efficiency at the highest power outputs.
The engine is most widely recognized for its application in the
Mitsubishi MT series tractors (MT30, MT33), the Case IH 2130, and the
Toro Reelmaster 4500-D commercial mowing equipment. The K4M combines a
cast iron cylinder block with an overhead valve (OHV) valvetrain and a
Bosch M-type in-line injection pump. Its robust construction and 22:1
compression ratio deliver reliable cold starting and extended service
intervals in demanding agricultural and industrial environments.
The Mitsubishi K4M occupies a specific market position as a compact yet
durable indirect injection diesel for off-highway equipment. The engine
displaces 1,995 cc achieved through bore and stroke dimensions of 84 mm
by 90 mm. This undersquare configuration produces modest power - 36 to
42 horsepower (27-31 kW) - but delivers a broad torque curve suited to
traction applications.
The swirl chamber (indirect injection) combustion system includes a
pre-combustion chamber cast into the cylinder head, where fuel begins
burning before the flame front enters the main cylinder. This design
permits the use of lower injection pressures and produces quieter
combustion compared to direct injection engines, an advantage for
operator comfort in turf care applications.
The valvetrain uses pushrods and rocker arms actuated by a camshaft
located high in the cylinder block. Mechanical lifters (solid tappets)
require periodic manual valve lash adjustment every 500 operating hours.
The fuel system employs an in-line injection pump, commonly a Bosch
M-type or a Mitsubishi-built equivalent, with individual plungers for
each cylinder. This mechanical system, while lacking electronic
precision, offers excellent field serviceability.
The forced lubrication system uses a trochoid-type pump mounted on the
camshaft or crankshaft, circulating oil through a full-flow filter. The
engine accepts a maximum compression pressure of 30 kg/cm2 (427 psi) at
280 cranking rpm. With regular maintenance - including 250-hour oil
changes and 500-hour valve adjustments - the K4M frequently achieves
8,000 to 10,000 operating hours before requiring major overhaul in
agricultural service.
Engine Type: 4-cycle, Overhead Valve (OHV), Inline-4 diesel
Valvetrain: OHV, 8 valves (2 per cylinder) with pushrods and rocker arms
Aspiration: Naturally Aspirated
Displacement: 1,995 cc (2.0 L, 121.7 cu.in)
Bore: 84.0 mm (3.31 in)
Stroke: 90.0 mm (3.54 in)
Compression Ratio: 22:1
Combustion System: Swirl chamber (Indirect injection)
Firing Order: 1-3-4-2
Maximum Power: 36-42 hp (27-31 kW) @ 2,200-2,400 rpm
Maximum Torque: 140-155 Nm (103-114 lb-ft) @ 1,600-1,800 rpm
Maximum Governed Speed: 2,600 rpm (no-load)
Low Idle Speed: 650-750 rpm
Compression Pressure (Standard): 30 kg/cm2 (427 psi) @ 280 rpm
Compression Pressure (Minimum Service Limit): 25 kg/cm2 (356 psi)
The cylinder block is a monobloc casting manufactured from high-strength
grey cast iron with additional alloying elements for wear resistance.
The block uses an open-deck design with integral, non-replaceable
cylinder bores machined directly into the casting. Each bore receives a
final plateau honing finish to promote rapid piston ring seating and
long-term oil control. The block is of a deep-skirted design, extending
below the crankshaft centerline to enhance structural rigidity.
Five main bearing bulkheads are cast integrally with the block,
supporting a forged or nodular cast iron crankshaft. The crankcase
incorporates cast-in oil galleries on the intake side, feeding
pressurized oil to the main bearings and cylinder head. Engine mounting
bosses are cast into the block sides and flywheel housing. The timing
gear housing, integral to the front of the block, contains the gear
train that drives the camshaft, injection pump, and other accessories.
The block does not use replaceable cylinder liners; over-boring during
overhaul is possible within specified service limits.
The cylinder head is a single, cross-flow casting manufactured from
high-strength grey cast iron. The combustion system uses individual
swirl chambers (pre-combustion chambers) for each cylinder. Each swirl
chamber is a separate steel insert pressed into the cylinder head,
connected to the main cylinder by a small passage. The injector nozzle
is positioned to spray fuel into the swirl chamber, where partial
combustion occurs before expanding into the main cylinder. This indirect
injection design reduces combustion noise and allows operation with
lower injection pressures.
The cylinder head carries two valves per cylinder: one intake and one
exhaust. Valves are constructed from heat-resistant silichrome steel,
with exhaust valves featuring stellite-faced tips for wear resistance.
Valve seats are pressed-in, heat-treated alloy steel inserts. The
valvetrain operates via a camshaft located high in the cylinder block on
the right side. Mechanical lifters (solid tappets) follow the camshaft
lobes and transfer motion through hardened pushrods to cast-iron rocker
arms.
The rocker arms pivot on a through-shaft mounted above the cylinder
head. Valve lash adjustment uses a screw-and-locknut arrangement at the
rocker arm-to-valve stem interface. Adjustments are performed with the
engine cold. The cylinder head gasket is a steel-reinforced composite
design with a fire ring around each cylinder.
The fuel system is a mechanical indirect injection design. An in-line
injection pump, commonly a Bosch M-type or Mitsubishi MD-series pump, is
mounted on the cylinder block and driven by the timing gear train. The
pump contains four individual pumping plungers, one per cylinder,
arranged in a straight line. Each plunger is actuated by a camshaft
within the pump housing. The pump includes a mechanical centrifugal
governor that maintains engine speed under varying loads by adjusting
fuel delivery. A manual fuel shut-off lever stops the engine by cutting
fuel supply.
A mechanical diaphragm-type or gear-type feed pump, mounted on the
injection pump body, draws fuel from the tank and delivers it through a
water-separating fuel filter to the injection pump. Each cylinder has a
throttle-type nozzle (pintle or hole-type injector) mounted vertically
in the cylinder head, positioned to spray into the swirl chamber.
Injectors are spring-loaded, calibrated to open at a precise pressure.
Excess fuel not injected returns to the fuel tank through a return line
for pump cooling. Injection timing is set to 21° before top dead center
(BTDC) as a baseline, measured by observing fuel flow at the delivery
valve or using a timing light on the marks.
The lubrication system is a forced, full-flow wet-sump design. A
trochoid-type oil pump is mounted internally on the camshaft or
crankshaft within the timing gear case. The trochoid pump uses an inner
rotor with lobe-like teeth rotating inside an outer rotor, providing
consistent flow with low pulsation. The pump draws oil through a
screened pickup tube from a stamped steel or cast aluminum oil pan. Oil
capacity ranges from 5.0 to 5.5 liters (5.3-5.8 qt) depending on the oil
pan depth.
Oil passes through the pump and then through a full-flow, spin-on oil
filter mounted on the cylinder block. An integral bypass valve within
the filter housing allows unfiltered oil to circulate if the filter
becomes restricted. From the filter, pressurized oil enters the main oil
gallery, a longitudinal passage drilled through the left side of the
cylinder block. The main gallery distributes oil to all five main
bearings through cross-drilled passages. Connecting rod bearings receive
oil from the main bearings via diagonal passages drilled through the
crankshaft.
A separate vertical passage in the cylinder block carries oil to the
cylinder head, where it reaches the rocker shaft and rocker arms through
hollow pushrods or external lines. Oil pressure is regulated by a
spring-loaded relief valve located on the oil pump housing or within the
main gallery, which diverts excess oil back to the sump. The recommended
oil grade is SAE 10W-30 or 15W-40, API classification CD or better.
The cooling system is a sealed, pressurized, and thermostatically
controlled liquid-cooled design. Coolant circulation is driven by a
belt-driven centrifugal water pump mounted on the front of the cylinder
block. The water pump is driven by a V-belt from the crankshaft pulley,
which also drives the alternator and cooling fan. Coolant flows from the
water pump into the cylinder block water jacket, where it circulates
around the cylinders and then rises through transfer passages into the
cylinder head.
The cylinder head incorporates integrated coolant passages that direct
flow around the swirl chambers, exhaust valve seats, and injector
nozzles. A wax-pellet thermostat is located in a housing at the front of
the cylinder head. The thermostat is rated to begin opening at 76-82°C
(169-180°F), depending on the specific application and market. When the
thermostat is closed, coolant recirculates within the engine for rapid
warm-up.
When open, coolant flows to the top tank of a down-flow radiator. A
fixed-blade or viscous clutch cooling fan is mounted on the water pump
hub. A coolant recovery reservoir connected to the radiator filler neck
captures overflow during expansion. System pressure is maintained by a
radiator cap rated for 0.7-1.0 bar (10-15 psi).
| Intake and Exhaust Systems |
Intake System: Air enters through a dry-type, two-stage air cleaner with
a replaceable paper filter element and an integral dust ejector. The air
cleaner includes a restriction indicator that signals when the element
requires replacement. The intake manifold distributes clean air evenly
to all four cylinders.
Exhaust System: A single cast-iron exhaust manifold collects exhaust
gases from all four cylinders. The manifold routes exhaust upward or to
the side, connecting to a vertical exhaust stack on tractors or a
muffler system on turf equipment. Some industrial applications include a
spark arrestor for fire safety.
Electrical System: The engine is equipped with a 12-volt,
negative-ground electrical system. A 12-volt, 2.0 kW starter motor
engages the flywheel ring gear through a solenoid. The charging system
uses a 12-volt alternator with output ranging from 35 amperes (base
configuration) to 50 amperes (high-output option for equipment with
multiple electrical loads). The electrical system supplies power for the
starter motor, fuel shut-off solenoid, instrumentation, and any chassis
or implement lighting.
Starting Aid: For cold weather starting, most K4M installations include
glow plugs (pre-heaters) mounted in the swirl chamber or intake
manifold. A glow plug controller or manual switch activates the plugs
for 5-15 seconds before cranking.
Fuel Shut-off System: The injection pump is equipped with an
electrically operated fuel shut-off solenoid (stop solenoid). When the
ignition key is turned to the OFF position, the solenoid closes, cutting
fuel supply and stopping the engine. A manual shut-off lever is also
provided on the injection pump for emergency stops or troubleshooting.
Governor System: A mechanical centrifugal governor is integral to the
injection pump. Flyweights inside the governor housing rotate with the
pump shaft. The operator’s throttle lever sets a spring force against
the governor. Any deviation from the desired engine speed changes the
centrifugal force on the flyweights, which moves a control sleeve and
rotates a metering valve within the injection pump.
Overall Engine Length (Front Pulley to Flywheel Housing): 730 mm (28.7
in)
Overall Engine Width: 500 mm (19.7 in)
Overall Engine Height (From Oil Pan Rail to Valve Cover Top): 635 mm
(25.0 in)
Dry Weight (Complete, No Fluids, No Flywheel): 190 kg (419 lb)
Weight (With Fluids, Flywheel, Starter, Alternator): 210 kg (463 lb)
Engine Oil:
Grade: SAE 10W-30 or SAE 15W-40 (diesel-rated, API CD, CE, or CF-4).
Oil Capacity (With Filter, Standard Pan): 5.0 L (5.3 qt).
Oil Capacity (With Filter, Deep Pan): 5.5 L (5.8 qt).
Normal Oil Pressure (Rated Speed, Hot): 300-450 kPa (44-65 psi).
Minimum Oil Pressure (Hot Idle): 70 kPa (10 psi).
Engine Oil Change Interval: Change every 250 hours or annually.
Engine Oil Change Interval: Change every 150 hours for severe duty.
Oil Filter Change Interval: Replace at every oil change.
Cooling System:
Coolant Type: Diesel-rated ethylene glycol antifreeze (50/50 mix with
distilled water).
Total System Capacity (Engine Only): 3.8 L (4.0 qt).
Total System Capacity (With Radiator and Hoses): 6.0-7.5 L (6.3-7.9 qt),
radiator dependent.
Thermostat Opening Temperature: 76-82°C (169-180°F), application
dependent.
Radiator Cap Pressure Rating: 0.7-1.0 bar (10-15 psi).
Coolant Change Interval: Drain, flush, and refill every 1,000 operating
hours or every 2 years.
Valve Clearance (Cold Engine, Ambient
Temperature):
Intake: 0.25 mm (0.010 in).
Exhaust: 0.25 mm (0.010 in).
Valve Adjustment Interval: Inspect and adjust every 500 operating hours
or annually.
Fuel Filter Change Interval (Water Separator and Secondary): Replace
every 250 operating hours or annually. Drain water from separator weekly
in humid climates. Air Cleaner Element Replacement: Replace primary
paper element when restriction indicator shows red or every 250 hours.
Service dust ejector daily in dusty conditions.
Injection Timing Check: Verify injection timing (21° BTDC baseline)
every 1,000 operating hours using a timing light on flywheel marks or a
dial indicator on the injection pump. Injector Testing: Test injector
opening pressure and spray pattern every 1,000 operating hours.
Recalibrate or replace as needed.
Compression Test: Perform compression test every 1,500 operating hours.
Standard value: 30 kg/cm2 (427 psi) @ 280 rpm. Service limit: 25 kg/cm2
(356 psi) with maximum variation between cylinders of 2 kg/cm2 (28 psi).
Cylinder Head Bolts (M14): 147-157 Nm (108.4-115.7 lb-ft) final torque.
Cylinder Head Bolts (Tappet side bolts): 98-108 Nm (72.3-79.5 lb-ft).
Connecting Rod Cap Nuts: 54-59 Nm (39.8-43.4 lb-ft).
Main Bearing Cap Bolts: 98-108 Nm (72.3-79.5 lb-ft).
Flywheel Bolts (to Crankshaft Flange): 83 ± 5 Nm (61.5 ± 3.6 lb-ft).
Crankshaft Pulley Bolt (Front Damper): 180-200 Nm (133-148 lb-ft).
Camshaft Drive Gear Bolt: 80-90 Nm (59-66 lb-ft).
Injection Pump Mounting Nuts (to Timing Gear Housing): 25-30 Nm (18-22
lb-ft).
High-Pressure Injection Lines (Injector End, Pump End): 25-30 Nm (18-22
lb-ft).
Injector Hold-Down Clamp Bolts: 25-30 Nm (18-22 lb-ft).
Intake Manifold Bolts: 20-25 Nm (15-18 lb-ft).
Exhaust Manifold Nuts: 30-35 Nm (22-26 lb-ft).
Oil Pan Bolts (Stamped Steel Pan): 12-15 Nm (9-11 lb-ft).
Valve Cover Bolts: 8-10 Nm (6-7 lb-ft).
Thermostat Housing Bolts: 18-22 Nm (13-16 lb-ft).
Water Pump Mounting Bolts: 20-25 Nm (15-18 lb-ft).
Starter Motor Mounting Bolts: 40-45 Nm (30-33 lb-ft).
Alternator Mounting Bracket Bolts: 30-35 Nm (22-26 lb-ft).
Glow Plugs (If Equipped): 15-20 Nm (11-15 lb-ft).
Oil Drain Plug (Oil Pan): 40-50 Nm (30-37 lb-ft).
The Mitsubishi K4M engine was utilized as the standard diesel powertrain
for the following vehicles and equipment across global markets.
Agricultural Tractors:
Mitsubishi MT30 (30 hp tractor, 1985-1995).
Mitsubishi MT33 (33 hp tractor).
Mitsubishi MT32 and MT36 (variants for export markets).
Case IH 2130 (Case International Harvester rebadged Mitsubishi tractor).
Satoh S-470 (Satoh was a Mitsubishi affiliate brand for some export
tractors).
Construction and Industrial Equipment:
Mitsubishi MM30 and MM35 mid-sized excavators (mini-excavators).
Mitsubishi FD15 and FD20 forklifts (2.0-2.5 ton capacity models).
Various industrial power units for pumps, generators, and compressors.
Turf and Commercial Mowing Equipment:
Toro Reelmaster 4500-D (heavy-duty reel mower for golf courses and
athletic fields).
Toro Groundsmaster 300 series (some variants).
Jacobsen HR-901 and Super Cert 99 mowers (limited applications).
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